The present invention relates to a vacuum valve control device for a vacuum valve installed in a vacuum type sewage collection system or a vacuum type chemicals transporting apparatus, the valve body of which is driven by a pressure difference between vacuum and atmosphere. More particularly, the present invention relates to a vacuum valve control device for controlling vacuum used for opening and closing the valve body.
Usually, sewage discharged from every home flows to a sewage disposal plant by the action of natural flow. However, in this natural flow type sewage collection system, the construction of sewer pipes is restricted by geography and the condition of the ground, and further the drain tends to be stopped up. For this reason, recently, attention has been given to a vacuum type sewage collection system in which sewage discharged from every home is forcibly transported by the action of vacuum.
This vacuum type sewage collection system includes: a vacuum valve unit in which sewage discharged from each home is stored when it flows by the action of natural flow; and a vacuum station by which sewage is collected from the vacuum valve unit through a vacuum pipe.
A vacuum valve unit is disclosed, for example, in U.S. Pat. No. 5,069,243. The vacuum valve unit disclosed in the above patent includes: a suction pipe, one end of which is dipped in sewage in the sewage tank; a vacuum valve, the pipe-shaped communicating portion of which is connected with the other end of the suction pipe; and a vacuum discharge pipe connected with the communicating portion, wherein this vacuum discharge pipe is connected with a vacuum pump disposed in a vacuum station through a vacuum pipe. In the vacuum valve, the pipe-shaped communicating portion can be opened and closed when a valve body disposed in the pipe-shaped communicating portion is operated. The vacuum pipe is maintained to be in a vacuum condition at all times by the action of the vacuum pump through the vacuum pipe. When a predetermined amount of sewage is stored in the sewage tank, the valve body of the vacuum valve is opened by a pressure difference between the vacuum in the vacuum discharge pipe and the atmosphere, so that the pipe-shaped communicating portion can be opened. Due to the foregoing, the vacuum discharge pipe in a vacuum condition is communicated with the suction pipe, so that sewage in the sewage tank is sucked into the vacuum discharge pipe by the action of vacuum, and transported to the vacuum station through the vacuum pipe.
The valve body disposed in the communicating portion of the vacuum valve usually closes the communicating portion. When the valve operating chamber is put into a vacuum condition, the valve body is pulled so that the communicating portion can be opened. The vacuum condition in the valve operating chamber is controlled by the vacuum valve control device.
This vacuum valve control device is connected with a liquid level detecting pipe, the lower end of which is dipped in the sewage in the sewage tank. When the liquid level of sewage is changed, the pressure in the liquid level detecting pipe is changed, so that a liquid level detecting diaphragm provided in the vacuum valve control device is resiliently deformed. Due to the deformation of the liquid detecting diaphragm, a detecting valve for introducing a vacuum into the vacuum valve control device is operated. Therefore, vacuum is activated on a changeover valve disposed in the vacuum control valve. Due to the foregoing, the changeover valve can be changed over, so that the vacuum discharge pipe is communicated with the valve operating chamber of the vacuum valve. Accordingly, this valve operating chamber is put in a vacuum condition. When the valve operating chamber is put in a vacuum condition, the valve body is pulled, and the communicating portion is opened.
As a result of the foregoing, the vacuum discharge pipe in a vacuum condition is communicated with the suction pipe, so that the inside of the suction pipe is also put in a vacuum condition. Accordingly, sewage in the sewage tank is quickly sucked into the suction pipe and vacuum discharge pipe. Then the sewage is transported into a sewage collection tank in the vacuum station through the vacuum pipe.
When sewage in the sewage tank is sucked in a moment, the liquid level detecting diaphragm of the vacuum valve control device gradually returns to the original condition. Due to the foregoing, the operation of the detecting valve is released, and the communication between the inside of the vacuum valve control device and the vacuum discharge pipe is intercepted, and at the same time the atmosphere is introduced into the vacuum valve control device. Then the changeover valve is changed over, so that the atmosphere is introduced into the valve operating chamber of the vacuum valve.
According to above mentioned U.S. Pat. No. 5,069,243, a damping mechanism is provided, by which the liquid level detecting diaphragm is prevented from being resiliently deformed in the case where sewage in the sewage tank is discharged by the vacuum discharge pipe and the resilient deformation of the liquid level detecting diaphragm is released. This damping diaphragm includes: a pressure adjusting chamber provided between the liquid level detecting pipe and the liquid level detecting diaphragm; and a damping diaphragm provided between the pressure adjusting chamber and the liquid level detecting diaphragm.
A minute through-hole is formed on this damping diaphragm so that the damping diaphragm is not deformed when the pressure in the liquid level detecting pipe is gradually increased. Therefore, the damping diaphragm is not resiliently deformed by an increase of pressure in the liquid level detecting pipe in the case where sewage is stored in the sewage tank. On the other hand, in the case where the liquid level detecting diaphragm is resiliently deformed after sewage in the sewage tank has been discharged and the resilient deformation of the liquid level detecting diaphragm has been released, the damping diaphragm is resiliently deformed, so that the communication between the pressure adjusting chamber and the liquid level detecting diaphragm is intercepted. As a result, the liquid level detecting diaphragm is prevented from being resiliently deformed. Therefore, there is no possibility that the detecting valve is activated again, and there is no possibility that the vacuum valve is opened.
In the vacuum sewage collecting apparatus described above, sewage in the sewage tank is sucked and discharged in a moment. Therefore, the liquid level of the sewage tank is suddenly lowered. As a result, the liquid level of the liquid level detecting pipe is also lowered so that the pressure in the liquid level detecting pipe is also suddenly lowered. However, as described above, since the damping diaphragm is provided between the liquid level detecting pipe and the pressure adjusting chamber, the pressure in the pressure adjusting chamber is released only through a minute through-hole when the pressure in the liquid detecting pipe is lowered. Therefore, it takes time to cancel the resilient deformation of the liquid level detecting diaphragm. As a result, even when sewage in the sewage tank is discharged, an excessive amount of air is sucked and the degree of vacuum is lowered.
Further, in the vacuum valve control device, the vacuum force introduced into the pressure control chamber is released to the atmosphere by a needle valve.
However, in the conventional vacuum type sewage collecting system, as illustrated in FIG. 5, at a distant place from the vacuum station 2 for collecting sewage into the sewage collecting tank 1, the vacuum is lowered by the saw-tooth lift 4 provided in the vacuum pipe line 3. Therefore, in the case of an opening time adjusting mechanism having a needle valve provided in the controller of a conventional vacuum valve, the needle valves are respectively adjusted at adjacent and distant places in such a manner that the opening time of a vacuum valve located at a distant place is set longer so that an air/liquid ratio in the pipe line can be maintained in a particular range (disclosed in Japanese Unexamined Patent Publication (Kokai) Hei-2-292427). In the case where the vacuum valves are simultaneously opened, vacuum in the vacuum discharge pipe is lowered. When this condition frequently occurs, a sufficient amount of air is not supplied into the vacuum pipe line, so that a water plug grows in the lift portion, and the entire system is in trouble.
Furthermore, between an outer circumferential surface provided in the housing of the vacuum valve and an inner circumferential surface of the housing, a rolling diaphragm is disposed, by which the valve operating chamber in the housing is airtightly isolated. This rolling diaphragm is made of resilient rubber, and bent between the outer circumferential surface of the plunger and the inner circumferential surface of the housing so that the rolling diaphragm can be closely brought into contact with the outer circumferential surface of the plunger and the inner circumferential surface of the housing. In the case where the plunger is slid by the action of vacuum in the valve operating chamber in the housing, the rolling diaphragm is deformed so that the bent portion is moved in a sliding direction of the plunger. As described above, while a volume in the valve operating chamber is not changed, the plunger can be positively slid by the action of the rolling diaphragm when vacuum is activated.
Usually, a portion close to the bent portion of the rolling diaphragm is not closely contacted with the inner circumferential surface of the housing, but the portion is contacted with the rolling diaphragm which is closely contacted with the outer circumferential surface of the plunger. When one portion of the rolling diaphragm is contacted with another portion with pressure as described above, there is a possibility that the contacting portion is rubbed and worn away in the case where the contacting portion is moved in accordance with the sliding movement of the plunger. When the rolling diaphragm is worn away, there is a possibility that airtightness of the rolling diaphragm is deteriorated. When airtightness of the rolling diaphragm is deteriorated, airtightness of the valve operating chamber can not be maintained, and the plunger can not be driven even when the valve operating chamber is put in a vacuum condition.
Therefore, in order to suppress the abrasion of the rolling diaphragm, a method is put into practical use, in which a surface of the rolling diaphragm is coated with lubricant such as silicon grease or silicon oil. However, the coated lubricant permeates into the rolling diaphragm made of resilient material, so that the effect of the lubricant can not be exerted over a long period of time. For this reason, the rolling diaphragm must be replaced in a short period of time.